The use of chucks to hold workpieces on machine tools, such as lathes, milling machines, turning machines and the like, is almost as old as machine tools themselves. Early lathes, for example, were used to turn a workpiece while applying a tool, such as a blade, to craft the workpiece into a desirable form. Chucks were employed early on to hold the workpiece in place to keep the workpiece from slipping during a machining operation. If the workpiece moved in any way while being turned on the machine, the workpiece could easily be damaged, requiring the operator to start a part over again using a new workpiece. If the workpiece slipped or, even worse, came loose from the chuck, the workpiece could also pose a threat to the operator. Accordingly, it has long been desirable to use chucks that hold the workpiece securely and safely in the machine tool during operation of the machine.
A key issue with chucks, however, is adjustability. Chucks may need to hold workpieces of varying shape and size. Most early lathes were used to turn and craft round parts, such as furniture legs and spindles. Such round parts were easy to hold securely on the machine. Additionally, little adjustment of the chucks was needed when holding standard round parts. Typically, a chuck with independently adjustable master jaws was provided to hold the workpiece. Such a chuck design was acceptable so long as production levels were low and manageable for the operator. With low production levels, the operator could make sure the workpiece is properly centered and adequately secured before starting the machine.
As time went on, mass production of parts became more desirable and, thus, operators were required to increase the speed with which parts were manufactured. As a result, operators needed to change over from a completed part to a new workpiece quickly. The use of independently adjustable jaws was not desirable for mass production because too much time was needed to adjust each jaw to center a new workpiece. Accordingly, independently adjustable master jaws were replaced with chucks using self-centering jaws. Positioning and gripping the workpiece was quicker and easier with self-centering jaws because the operator no longer needed to adjust each jaw separately to center the workpiece and could quickly get the machine operating with less downtime required for set-up.
Eventually, machine tools began to be used to manufacture oddly shaped parts, such as sand castings. Safe and efficient operation of the machine tool required that all parts, regardless of shape, be held securely and safely during operation of the machine. The ease with which the jaws of the chuck could hold round parts did not carry over to such oddly shaped parts. Accordingly, new jaw designs were needed to ensure that any workpiece, regardless of shape and size, could be held in place during machine operation without affecting production or safety. That is, different part designs, depending on shape and size, may require specifically designed chuck jaws in order to be held securely and safely during operation. Commonly, variations in workpiece shape and size require a separate, customized set of chuck jaws. Accordingly, use of a single machine would be inefficient and less time effective if the chuck jaws needed to be constantly changed from part to part. Each change over would result in downtime while one set of chuck jaws were removed and replaced by another set of chuck jaws, depending on the part being crafted. Moreover, the requirement to use different chuck jaws for different shaped or sized parts could be expensive. A more efficient, less costly, and more versatile design is desired that can accommodate workpieces of various designs, shapes and sizes.
Removing and replacing chuck master jaws is also a legitimate concern for the machine operator. Every time a chuck master jaw is removed, use of the machine is affected because downtime eats into manufacturing time. Chuck master jaws may need to be removed regardless of whether the size and shape of the workpiece changes. For example, chuck master jaws often need to be removed for repair or replacement. The downtime for repair or replacement often depends on the damage to the chuck. There is a desire to have a chuck design that facilitates repair and, where needed, replacement, without greatly affecting operation and efficiency of the machine tool, in general.
A solution to this problem of needing multiple sets of chuck jaws or alternatively, multiple machines, to be able to produce various parts was the development of the two-piece adjustable master jaw. This design provided greater flexibility for the machine to accommodate workpieces of varying shape and size without the need to slow down operation time by needing to change the chuck. Although various methods of adjusting the master jaw have been tried, the most common design in use today is a two-piece master jaw with a lower operating jaw and an upper adjustable jaw. An adjustable screw is trapped in the lower operating jaw and a half-diameter thread is cut in the upper jaw. The upper jaw sits atop the lower operating jaw and may be adjusted using the interaction between the adjustable screw and the upper jaw to actuate the upper jaw to a desired position. Commonly, a machine tool comprises multiple upper master jaws, all of which can be adjusted to center and hold a workpiece securely for machining.
Due to forces being applied on the upper master jaw in such a set-up, the thread on the adjustable screw must be the square cut style of thread. This style of thread is difficult to machine on an adjustable screw and very difficult to machine in the upper master jaw in order to accommodate the adjustable screw, as only a half-diameter of a thread is typically machined into the upper master jaw. Most other types of threads, for example, those manufactured with sloped sides, often can not handle the forces exerted through use of the chuck. That is, when pressure is applied on the upper master jaw in intended operation, the adjustable screw is susceptible to binding in the lower operating jaw. Square cut style thread is less economical, forms weaker contact and is harder to repair or replace than some other thread designs.
The two-piece adjustable master jaw design of the prior art solves the problem of gripping workpieces with large variations but has its own set of problems. As already stated, manufacturing of the adjustable screw and upper master jaw is difficult and expensive. Also, after the chuck has been in use for a period of time, it can become damaged or worn and, thus, need to be repaired. Repair of the chuck requires that the chuck be taken out of production and rebuilt. The rebuilding process almost always requires manufacturing a new adjustable screw and replacing the upper master jaw with a new one. This becomes very expensive and time consuming. In particular, the wear caused by moving the adjustable screw relative to the upper master jaw often decreases the integrity of the connection between the upper master jaw and the chuck before significant wear occurs to other portions of the upper master jaw. However, because the upper master jaw, as known in the prior art, is of unitary construction, the entire upper master jaw needs to be repaired.
In view of the foregoing, there is a need for a chuck design that can accommodate variously shaped and sized workpieces and be adjusted without affecting operational efficiency of the machine. The present invention was developed to eliminate the problems of existing chuck designs by providing an adjustable cartridge assembly for connecting the lower operating jaw to the upper master jaw while holding a workpiece securely and safely in a machine tool.